Microvessel (capillary, precapillary arteriole, postcapillary venule) fragments from human, bovine, and canine retinas will be isolated and either used immediately for biochemical and anatomic studies, or will be placed in tissue culture medium to allow cellular proliferation. Previous studies indicate that only the intramural pericytes grow under these conditions. Attempts will be made to find conditions that permit proliferation of endothelial cells, by manipulating 02 and glucose concentrations, and by adding various hormonal and other chemical factors, or vitreous fractions. Transmission and scanning electron microscopy will be performed on freshly isolated microvessels and on vascular cells growing in culture media. Similar studies will be performed on microvessels from retina and other organs obtained postmortem from diabetic and nondiabetic humans to determine if the vascular lesions of human diabetic retinopathy occur in other tissues as well. Biochemical studies will concentrate initially on examination of aldose reductase activity, which has been implicated in the pathogenesis of diabetic complications in the lens and peripheral nervous system, and of the glucosyl and galactosyltransferases that may play a role in vascular basement membrane synthesis. Biochemical, histochemical, and autoradiographic studies will be employed to search for the presence and cellular localization of insulin receptors on pericytes and endothelial cells, and transport systems for glucose and amino acids in the cell membranes. In vivo investigations using autoradiographic techniques will be conducted in addition to tissue culture studies to search for agents that induce endothelial cell proliferation and might thus produce models of proliferaive retinopathy. Comparison studies will utilize microvessels from brain, renal glomeruli, and other organs. Results of these investigations will be useful in understanding the physiology of normal retinal microvessels, and the pathogenesis of retinal vascular disorders such as diabetic retinopathy.